Embodiments of the present invention generally relate to phase sensing devices used in applications such as microscopy and photography. More specifically, certain embodiments relate to a wavefront imaging sensor (WIS) configured to measure phase variations and/or amplitude variations of a light field in a high Fresnel number regime.
A light field contains two primary sets of characteristics—amplitude/intensity and phase front variations. At present, commercial optical sensors are designed to operate much like our retina and are only responsive to light field amplitude/intensity variations.
The phase of light is very important for imaging because many objects, such as transparent organisms and cells, only significantly modulate the phase of transmitted light and do not change the amplitude/intensity much. Sometimes, contrast agents (e.g., stains) can be used to generate amplitude/intensity variations in these transparent objects, however staining involves preparation and can damage specimens. For this reason and others, phase microscopes are highly valued in biomedical applications for their ability to render contrast based on refractive index variations in unstained biological samples. Such applications include field analyses of bloodborne and waterborne pathogens where cost considerations and ease-of-use are important, and analysis of biopsy sections to determine tumour margins during surgical procedures where rapid processing is critical. Phase microscopes are also useful where staining is undesirable or simply not an option. Such applications include examinations of oocytes and embryos during in-vitro fertilization procedures, and longitudinal imaging of live cells or organisms. Examples of these applications can be found in S. L. Stanley, “Amoebiasis,” Lancet 361, 1025-1034 (2003), M. M. Haglund, M. S. Berger, and D. W. Hochman, “Enhanced optical imaging of human gliomas and tumor margins,” Neurosurgery 38, 308-317 (1996), J. Vanblerkom, H. Bell, and G. Henry, “The occurrence, recognition and developmental fate of pseudo-multipronuclear eggs after in-vitro fertilization of human oocytes,” Hum. Reprod. 2, pp. 217-225 (1987) and R. J. Sommer, and P. W. Sternberg, “Changes of induction and competence during the evolution of vulva development in nematodes,” Science 265, 114-118 (1994), which are hereby incorporated by reference in their entirety for all purposes.
Conventional differential interference contrast (DIC) microscopes and, to a lesser extent, phase contrast microscopes and Hoffman phase microscopes have been the primary phase microscopes used in the past five decades. FIG. 1(a) is a schematic illustration of the underlying principle of a conventional DIC device (e.g., such as a conventional DIC microscope or camera). A conventional DIC device operates by interfering slightly displaced duplicate image light fields of polarized light. FIG. 1(b) is a schematic drawing of a conventional DIC device. An example of a phase contrast microscope can be found in F. Zernike, “Phase contrast, a new method for the microscopic observation of transparent objects,” Physics 9, 686-698 (1942). An example of a Hoffman phase microscope can be found in R. Hoffman, and L. Gross, “The modulation contrast microscope,” Nature 254, 586-588 (1975). An example of a conventional DIC microscope can be found in G. Nomarski, “New theory of image formation in differential interference microscopy,” Journal of the Optical Society of America 59, 1524-& (1969), and an imaging strategy used by a conventional DIC microscope can be found in “DIC,” http://www.microscopyu.com/articles/dic/dicindex.html, (2007). These three references are incorporated by reference in their entirety for all purposes.
However, these conventional phase microscopes have several limitations. One major limitation of the techniques used by these conventional devices is that phase variations are inextricably mixed with the amplitude/intensity variations that arise from absorption and/or scattering by an object. As a consequence of this entanglement of amplitude and phase information, these conventional techniques do not provide quantitative phase measurements. This limitation can introduce ambiguities in the rendered image of the object. Another limitation of conventional DIC devices is that they use polarized light and depend on the polarization in their phase-imaging strategies. Since polarized light must be used, conventional DIC devices generate images of birefringent samples, such as muscle sections and collagen matrices that typically suffer from significant artifacts. An example of a DIC microscope that uses polarization in its phase-imaging strategy can be found in B. C. Albensi, E. V. Ilkanich, G. Dini, and D. Janigro, “Elements of Scientific Visualization in Basic Neuroscience Research,” BioScience 54, 1127-1137 (2004), which is hereby incorporated by reference in its entirety for all purposes. Since polarized light must be used, these devices generate images of birefringent objects (e.g., potato starch storage granules) that typically suffer from significant artifacts. Furthermore, these techniques use elaborate and bulky optical arrangements that are expensive and require high maintenance. The relatively high cost of these systems prevents their broader use.
In recent years, other phase microscopy techniques have been developed such as 1) phase shifting interferometry schemes—where two or more interferograms with different phase shifts are acquired sequentially and a phase image is generated therefrom, 2) digital holography or Hilbert phase microscopy—where high frequency spatial fringes encoded on the interferogram are demodulated to generate the phase image, 3) swept-source phase microscopy—where modulation in the interferogram generated by a wavelength sweep can be processed to create a phase image, 4) Polarization quadrature microscopy—where phase images are generated by a polarization based quadrature interferometer, and 5) harmonically matched grating-based phase microscopy—which makes use of non-trivial phase shifts between the different diffraction orders from a harmonic combination grating to generate phase images. Examples of these phase microscopy techniques can be found in K. Creath, “Phase-measurement interferometry techniques,” Prog. Opt. 26, 44 (1988), K. J. Chalut, W. J. Brown, and A. Wax, “Quantitative phase microscopy with asynchronous digital holography,” Optics Express 15, 3047-3052 (2007), P. Marquet, B. Rappaz, P. J. Magistretti, E. Cuche, Y. Emery, T. Colomb, and C. Depeursinge, “Digital holographic microscopy: a noninvasive contrast imaging technique allowing quantitative visualization of living cells with subwavelength axial accuracy,” Optics Letters 30, 468-470 (2005), B. Rappaz, P. Marquet, E. Cuche, Y. Emery, C. Depeursinge, and P. J. Magistretti, “Measurement of the integral refractive index and dynamic cell morphometry of living cells with digital holographic microscopy,” Optics Express 13, 9361-9373 (2005), T. Ikeda, G. Popescu, R. R. Dasari, and M. S. Feld, “Hilbert phase microscopy for investigating fast dynamics in transparent systems,” Optics Letters 30, 1165-1167 (2005), G. Popescu, T. Ikeda, K. Goda, C. A. Best-Popescu, M. Laposata, S. Manley, R. R. Dasari, K. Badizadegan, and M. S. Feld, “Optical measurement of cell membrane tension,” Physical Review Letters 97 (2006), M. V. Sarunic, S. Weinberg, and J. A. Izatt, “Full-field swept-source phase microscopy,” Optics Letters 31, 1462-1464 (2006), D. O. Hogenboom, C. A. DiMarzio, T. J. Gaudette, A. J. Devaney, and S. C. Lindberg, “Three-dimensional images generated by quadrature interferometry,” Optics Letters 23, 783-785 (1998), Z. Yaqoob, J. G. Wu, X. Q. Cui, X. Heng, and C. H. Yang, “Harmonically-related diffraction gratings-based interferometer for quadrature phase measurements,” Optics Express 14, 8127-8137 (2006), and W. Choi, C. Fang-Yen, K. Badizadegan, S. Oh, N. Lue, R. R. Dasari, and M. S. Feld, “Tomographic phase microscopy,” Nature Methods 4, 717-719 (2007), which are hereby incorporated by reference in their entirety for all purposes. However, as with phase contrast and conventional DIC microscopy, these advanced methods contain significant optical elements and have relatively steep learning curves. In addition, these phase microscopy techniques invariably require the use of a laser source to provide coherent light.
Another technique for calculating optical phase includes collecting two or three successive images of the specimen around its focal plane. An example of this technique can be found in A. Barty, K. A. Nugent, D. Paganin, and A. Roberts, “Quantitative optical phase microscopy,” Optics Letters 23, 817-819 (1998), which is hereby incorporated by reference in its entirety for all purposes. This technique however, requires the physical actuation of the camera to be placed in three distinct positions in order to provide enough data to render a single phase image, and is therefore intrinsically limited in speed. In addition, the presence of a mechanical actuation system can also introduce undesirable vibrations to the microscope and potentially pose a challenge to sensitive experiments.